I just bought a complete new top end cylinder piston and rings and still him only getting 90 pounds of compression. I replace the whole top end because I was only get a 90 pounds of compression with the old top end not sure what's wrong. should I be getting 120 doing and 160 pounds of compression? the bike is a 90 cc adly blazer. I already had the head shaved 30 thousandths.

 

Are you the original owner? maybe someone bored it out, and you have too much piston to wall clearance. Mic the cylinder and piston, should be able to get specs from where you bought piston. Is there an auto decompressor that could be stuck? or a decomp. lever on the outside of the motor? Also check the endgap on the rings by pushing one down in the cylinder with the piston to make sure it is square to the cylinder, should be around .005 to .008 clearance on the ring ends, any more than that, and it could be blowing by the rings. Is this a 2 or 4 stroke? if a 4 stroke, make sure the valves are set correctly, even a tiny bit open would leak most of the compression out. If a 2 stroke, make sure the reeds seal tightly, could be blowing back out the carb.

 

The comp should go up once the rings seat.
You should have 120+.

 

OMG......Jack, you're ok !!... I saw that thread " LT80 dying", and I thought we were losing you !!.......lol.

 

The bike its two stroke. Iput a hetrick hop up kit with new carb, reed valve, intake and exhaust y to name a few. I just put a53mm big bore kit on because I was only getting 90 pounds of compression with the old top end. the big bore kit came with new jug, piston, rings so the top end is completely replaced. I still only get 90 pounds. How long before the rings set boosting compression? I changed the whole to end because of low compression now its the same just a little lost on why. The old top end ran great. Maybe bad compression tester? I left it on all night and it still shows 90 no lots of pressure over night. Should I get more than 90 pounds? Thanks for the help!

 

A comp gauge will not leak air till you press the valve.
Crank with a wide open throttle till the gauge peaks.
So what does Hetrick say?

 

Did you test compression right after rebuild? that could account for low psi if the rings did not seat in yet. Give it a good break in cycle,warm it up good with varying throttle, then a few blips and rests to get the rings to conform to the cylinder. If it doesnt improve after that, you may have other problems, but a matched hetrick kit should be good to go from the start, they don't make junk.

 

Hetrick has helped a ton setting this kit up. In just not sure why the compression did not increase with the brand new big bore kit. It should have at least changed right? This is my daughters bike and we ride on the dunes. Just trying to get the most out of it. Hope I didn't waste money on a kit we didn't need. Thanks for the help again. Does it take a while to increase? I seems to kick over harder now but not a ton.

 

Ok I t tested I it brand new. I will break it in today and test again. Hope that helps. I night the kit from another company who deals with Kasea a bunch. That guy told me the compression should reach at least 120 to when i bought it.